This invention relates to an instrument for the determination of radiation parameters of a focused charged-particle beam periodically guided over a target surface, especially in electron beam melting and vaporizing, the target surface being the surface of a melt. The invention also concerns measuring processes using this instrument.
In the use of electron beams it is frequently desired to detect the radiation parameters themselves, including the state of focus or focal spot diameter on the target surface, as well as the pattern of deflection of the electron beam on a target surface that is many times larger than the focus spot. The target surface can be scanned or swept by the electron beam along X-Y coordinates, for example.
The determination of radiation parameters is especially important in the vaporization of mixtures or alloys of materials having different melting and boiling points. In such cases, the individual components of the mixture or alloy are subject to different rates of vaporization, resulting in local changes of the composition of the mixture or alloy in the vaporizing crucible. Details concerning the behavior of molten alloys in vaporization as well as measures for their control are described in German published application No. 28 12 285.
A vacuum depositing process has become known in which an electrical probe is disposed above the surface and in the stream of the vapor of the vaporizing material, which is connected to an electrical indicating instrument. This probe serves, however, only for the determination of the rate of vaporization. Electrically charged vapor particles condense on the probe, and the charge that is yielded to the probe is a measure of the quantity of vapor per unit of time. The probe in question, however, is not placed in the path of an electron beam; it must not even be struck by the electron beam, because the latter would signal a non-existent high vaporization rate due to the charge which it would yield to the probe. This probe, therefore, is not an instrument for the determination of radiation parameters of a charged-particle beam.